[esnext] prototype runtime implementation for async functions

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 12507 matching lines @@
     default:
       return false;
   }
 }
 
 }  // namespace
 #endif
 
 
 void JSFunction::EnsureHasInitialMap(Handle<JSFunction> function) {
-  DCHECK(function->IsConstructor() || function->shared()->is_generator());
+  DCHECK(function->IsConstructor() || function->shared()->is_generator() ||
+         function->shared()->is_async());
   if (function->has_initial_map()) return;
   Isolate* isolate = function->GetIsolate();
 
   // The constructor should be compiled for the optimization hints to be
   // available.
   Compiler::Compile(function, Compiler::CLEAR_EXCEPTION);
 
   // First create a new map with the size and number of in-object properties
   // suggested by the function.
   InstanceType instance_type;
-  if (function->shared()->is_generator()) {
+  if (function->shared()->is_generator() || function->shared()->is_async()) {
     instance_type = JS_GENERATOR_OBJECT_TYPE;
   } else {
     instance_type = JS_OBJECT_TYPE;
   }
   int instance_size;
   int in_object_properties;
   function->CalculateInstanceSize(instance_type, 0, &instance_size,
                                   &in_object_properties);
 
   Handle<Map> map = isolate->factory()->NewMap(instance_type, instance_size);
@@ skipping 6511 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8